This is a solution to Advent of Code 2023 day 3, written in Raku.

https://adventofcode.com/2023/day/3

### Part One

The engine schematic (your puzzle input) consists of a visual representation of the engine. There are lots of numbers and symbols you don't really understand, but apparently any number adjacent to a symbol, even diagonally, is a "part number" and should be included in your sum.

What is the sum of all of the part numbers in the engine schematic?

```
my @s[140;140] = '3-input.txt'.IO.lines>>.comb;
my @offsets = (-1, -1), (-1, 0), (-1, 1),
( 0, -1), ( 0, 1),
( 1, -1), ( 1, 0), ( 1, 1);
my $symbols = <* / % - + # @ = & $>.any;
sub validate($x, $y) {
for @offsets -> ($dx, $dy) {
my $x2 = $x + $dx;
my $y2 = $y + $dy;
next if $x2 < 0 or $x2 > 139 or $y2 < 0 or $y2 > 139;
return True if @s[$y2;$x2] ~~ $symbols;
}
return False;
}
my $number = '';
my $valid = False;
my $total = 0;
for ^140 -> $y {
for ^140 -> $x {
given my $c = @s[$y;$x] {
when /\d/ {
$number ~= $c;
$valid = True if validate($x, $y);
}
default {
# say $number if $number && $valid;
$total += $number if $number && $valid;
$number = ""; $valid = False;
}
}
}
# say $number if $number && $valid;
$total += $number if $number && $valid;
$number = ''; $valid = False;
}
say "Sum of part numbers is {$total}";
```

Sum of part numbers is 514969

### Part Two

A gear is any * symbol that is adjacent to exactly two part numbers. Its gear ratio is the result of multiplying those two numbers together.

This time, you need to find the gear ratio of every gear and add them all up so that the engineer can figure out which gear needs to be replaced.

What is the sum of all of the gear ratios in your engine schematic?

```
my @s[140;140] = '3-input.txt'.IO.lines>>.comb;
my @offsets = (-1, -1), (-1, 0), (-1, 1),
( 0, -1), ( 0, 1),
( 1, -1), ( 1, 0), ( 1, 1);
sub adjacent-stars($x, $y) {
my @coords;
for @offsets -> ($dx, $dy) {
my $x2 = $x + $dx;
my $y2 = $y + $dy;
next if $x2 < 0 or $x2 > 139 or $y2 < 0 or $y2 > 139;
@coords.push("{$x2}:{$y2}") if @s[$y2;$x2] ~~ '*';
}
return @coords.Set.keys;
}
my $number = '';
my $coords = SetHash.new();
my %stars;
for ^140 -> $y {
for ^140 -> $x {
given my $c = @s[$y;$x] {
when /\d/ {
$number ~= $c;
my @a = adjacent-stars($x, $y);
$coords.set: @a;
}
default {
if $number { %stars{$_}.push($number) for $coords.keys; }
$number = '';
$coords = SetHash.new();
}
}
}
if $number { %stars{$_}.push($number) for $coords.keys; }
$number = '';
$coords = SetHash.new();
}
my $sum = [+] %stars.values.grep(+* == 2).map(-> @a { [*] @a });
say "Sum of gear ratios is {$sum}";
```

Sum of gear ratios is 78915902